From StarWars.com:
Collectors of the vintage line may have recognized something familiar in this week's episode of The Clone Wars, "Landing at Point Rain". The red deco of the Y-wing starfighters seen streaking across the Geonosian sky was first seen in 1979, as part of the second wave of vehicles in Kenner's popular die-cast line. The toy was actually based on early ILM Y-Wing model photos, which originally classified Y-wings as "Red" squadron and X-wings were "Blue" squadron. Ultimately, the X-wings were changed to red, and the red Y-wings became gold because the special effects technology of the day did not allow for the color blue to be used on models or objects that required them to be inserted onto a separate background.